Swim fin

ABSTRACT

A foot-mounted fin for use by skin divers and other swimmers, and including means to mount the fin on the foot of the swimmer and blade means to propel the swimmer through the water in response to kicking movement of the leg and foot. Water-intake (scoop) or mouth openings are provided in the top of the fin and adjacent the foot pocket or other mounting means. Water-outlet or jet-exhaust openings are provided at the tip of the blade and are directed away from the foot pocket. Wall means are provided to define nozzle passages connecting the water-intake openings with the jet-exhaust openings to thereby cause high-velocity jets of water to emanate from the blade tip, particularly during each downstroke of the foot of a swimmer who is in a face-down position.

I United States Patent MacNiel [451 Mar. 21, 1972 541 swI'M FIN [72]inventor: Douglas K. MacNiel, Costa Mesa, Calif.

{73] Assignee: U.S. Divers Co., Santa Ana, Calif.

[22] Filed: June 15, 1970 [21] Appl. No.: 46,061

[52] US. Cl ..9/309 [51] ..A63b 31/10 [58] Field of Search ..9/309. 301

[56] References Cited UNITED STATES PATENTS 3,183,529 5/1965 Beuchat..9/309 3,055,025 9/1962 Ferraro et a1 ..9/309 3,032,787 5/1962 Mazzeila..9/309 Primary Examiner-Milton Buchler Assistant Examiner-Gregory W.O'Connor Attorney-Gausewitz, Carr & Rothenberg [57] ABSTRACT Afoot-mounted fin for use by skin divers and other swimmers, andincluding means to mount the fin on the foot of the swimmer and blademeans to propel the swimmer through the water in response to kickingmovement of the leg and foot.

Water-intake (scoop) or mouth openings are provided in the top of thetin and adjacent the foot pocket or other mounting means. Water-outletor jet-exhaust openings are provided at the tip of the blade and aredirected away from the foot pocket. Wall means are provided to definenozzle passages connecting the water-intake openings with thejet-exhaust openings to thereby cause high-velocity jets of water toemanate from the blade tip, particularly during each downstroke of thefoot of a swimmer who is in a face-down position.

17 Claims, 5 Drawing Figures PATENTEDHARZI I972 3,649,979

SHEET 1 [1F 2 I'I'I'IIII IIIIII'IIII? IIAIIIII/II 'I'II'II" ("III'IIIIII'III'III INVENTOR. lira, 4 500414.; A/ M46N/EL 4 ORA/[VS PATENTED MAR21 I972 SHEET 2 [1F 2 swnvr FIN BACKGROUND OF THE INVENTION 1. Field ofthe Invention This invention relates to the field of foot-mounted swimfins used by sport swimmers, skin divers, professional divers, andothers, in order to increase the speed and efficiency of propulsionthrough the water.

2. Description of Prior Art It has previously been proposed to provideports, openings or passages through the blade of a swim fin, in attemptsto achieve advantages including increased propulsion, reducedturbulence, and reduced drag. Patents of this general type include US.Pat. Nos. 3,032,787, 3,055,025, and 3,183,529.

In no instance known to applicant, however, has it been proposed tocreate jets of water which pass outwardly from the tip region of theblade and in directions away from the foot pocket. More specifically, inno instance known to applicant has it been proposed to transmit waterfrom the top of the blade, adjacent the foot pocket, through passagemeans to water-outlet or jet-exhaust openings formed in the blade tipand directed away from the foot pocket. Such location of the jet-exhaustopenings produces major advantages described hereinafter.

I SUMMARY OF THE INVENTION The swim fin comprises a blade adapted to beemployed in propelling the swimmer through the water, means to securethe blade to the foot of a swimmer, and passage and orifice meansresponsive to the downward movement of the foot of a downwardly facingswimmer to cause jets of water to emanate from the tip of the blade andin directions away from the foot. Stated more specifically, relativelylarge-area water-scoop or mouth openings are formed in the top of theblade adjacent the inner end of the foot pocket, and relativelysmall-area water-outlet or jet-exhaust openings are formed in the tip ofthe blade. Nozzle passage means are formed through the blade from suchmouth openings to such jet-exhaust openings, and are of decreasingcross-sectional area in directions toward the jet-exhaust openings inorder to effect high-velocity jet exhaust therethrough.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a view, partially in sideelevation and partially in longitudinal section, showing the swim fin asmounted on the downwardly moving foot of a swimmer who is swimming in aface-down position;

FIG. 2 is a top plan view of the fin;

FIG. 3 is a longitudinal central section taken along line 3-3 of FIG. 2;and

FIGS. 4 and 5 are, respectively, transverse sectional views taken alonglines 4-4 and 5-5 ofFIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Throughout thisspecification and claims, such expressions as top of the blade" denotethat portion of the fin blade which is uppermost when the wearer isstanding on the ground. Conversely, the bottom of the blade is thatportion which is lowermost when the wearer is in standing position. Onlyone swim fin is described herein, it being understood that the swim finfor the other foot is identical or is substantially identical to the oneillustrated and described. All of the figures, excepting FIG. 1, showthe swim fin in its natural (unstressed and undeflected) condition.

Referring first to FIGS. 2 and 3, the'swim fin is illustrated tocomprise a blade adapted to be secured by mounting means I] to one foot12 (FIG. I) of the swimmer. The mounting means 11 is so constructed thatthe blade 10 is generally in a plane perpendicular to the leg of thewearer when the wearer is in standing position on the ground or othersupporting surface. The blade then extends away from the ankle of thewearer, in line with (and outwardly of) the instep and toes thereof.

Very desirably, the mounting means I1 comprises wall means 13 to definea foot pocket or chamber 14 adapted to receive the toes and the instepof the foot 12. It is to be understood that additional wall means, notshown, may be provided to enclose the ankle and/or heel.

In the illustrated embodiment, a heel strap 15 (FIG. 1) extends aroundthe heel of the wearer and is connected at its ends, through adjustableconnections, to lugs or ears 16 formed integrally on the sides of wallmeans 13.

Side ribs 17 are provided along the side edge portions of the blade 10and of wall means 13. The end regions of the side ribs 17 may begenerally parallel to each other, as shown in FIG. 2, but the centralregions thereof diverge substantially and in a direction away from theankle of the wearer. Thus, the blade 10 is caused to be substantiallywider than is the mounting meansll.

Mounted in equally spaced relationship intermediate the forward portionsof side ribs 17 are intermediate ribs 18. Such ribs are parallel to eachother and extend forwardly from the wall means 13 which defines the footpocket 14. Stated more definitely, the intermediate ribs 18 extendforwardly from the toereceiving portions of wall means 13. In theillustrated embodiment, there are two such intermediate ribs 18, and thespacing between such ribs is approximately equal to the spacing betweeneither of such ribs and the adjacent side rib 17.

The blade 10 comprises, in addition to the various ribs, a bottom wall20 which covers the entire bottom and forward portion of the swim fin.Such wall 20 merges at a thickened portion 21 (FIG. 3) with the bottomportion of the wall means 13. The bottom wall 20 thus extends to thewall means for defining the foot pocket.

A top wall 22 is provided in spaced relationship from bottom wall 20,and covers the entire region of the fin blade 10 forwardly of thetop-wall edges 23 illustrated in FIGS. 2 and 3. Such edges 23 are spaceda substantial distance forwardly from the wall means 13.

Referring particularly to FIGS. 4 and 5, each of the top and bottomwalls 22 and 20 is integral with all of the ribs 17 and 18, such ribsserving to maintain the walls 20 and 22 spaced from each other asillustrated. The ribs 17 and 18 not only extend between the walls butalso extend above and below the walls in order to increase the strengthof the ribs and also to provide deflector or baffle means for guidingthe water as it flows along the exterior surfaces of walls 20 and 22.

As shown in FIG. 4, the ribs 17 and 18 are relatively large and thick atregions adjacent the wall means 13. From such thick portions, the ribstaper progressively in a forward direction and become smaller asillustrated in FIG. 5. Thus, the walls 20 and 22 come progressivelycloser to each other and, additionally, the blade portions remote fromthe foot pocket are more flexible than are the blade portions adjacentthereto.

Walls 20 and 22, and theribs l7 and 18, cooperate with each other todefine three nozzle passages 24, 25 and 26 (FIGS. 3-5). Passage 24 isgenerally rectangular in section and is defined between a side rib 17and the adjacent intermediate rib 18, and also between the portions oftop and bottom walls 22 and 20 extending between such ribs.Correspondingly, passage 26 is defined between the remaining side rib l7and the adjacent intermediate rib 18, as well as between the wallportions 22 and '20 extending between such ribs. The central passage 25is formed between the two intermediate ribs 18 and between the top andbottom wall portions 22 and 20 extending between such ribs.

Since the walls 22 and 20 are spaced far from each other relativelyadjacent the wall means 13, the noulepassages 24-26 have relativelylarge cross-sectional areas adjacent such wall means. Thecross-sectional areas of the passages 24-26 progressively diminish in adirection away from the wall means 13, becoming minimum adjacent the tipregions of the blade (namely, those regions farthest from the ankle ofthe wearer). Thus, in FIG. 5 each of the passages 24-26 is illustratedas being relatively wide but thin (that is to say, there is only a shortdistance between the opposed portions of walls 20 and 22).

The ends of passages 24-26 remote from wall means 13 constitutewater-outlet or jet-exhaust openings or orifices 27 (FIG. 3) which aredirected forwardly and directly away from the wall means 13. Statedotherwise, such jet-exhaust openings or orifices 27 direct watergenerally in the plane of the tip region of the blade 10, and away fromthe foot and ankle of the wearer.

The other ends of the nozzle passages 24-26, those closest to the wallmeans 13, constitute water-intake or mouth openings 28. The water-intakeor mouth openings 28 face generally upwardly, when the wearer is instanding position on a supporting surface, that is to say such openingsface up and approximately 90 away from the direction of facing ofjet-exhaust openings 27 when the wearer is standing on such surface.When the wearer is swimming through the water, in downwardly facingposition, the downstroke of the leg and foot causes water to enter themouth openings 28 and then pass around a gentle curve (formed by wallportions 29 and 30 shown in FIG. 3) to the tip regions of the blade forexhaust through jet-exhaust openings 27. The water not only passesaround the gentle curve but also rapidly accelerates due to theprogressively decreasing cross-sectional areas of the passages 24-26,the result being the efficient creation of three highvelocity jetexhausts from the tip of the blade and away from the ankle of thewearer.

The entire swim fin, excepting the heel strap and associated fastenermeans, is molded integrally from an elastomeric material such as naturalor synthetic rubber. The elastomeric material should be sufficientlyhard to prevent excessive deformation. For example, the shore hardnessmay be about 70. The present swim fin is characterized by the advantagethat, despite the presence of passages 24-26, molding may be readilyeffected.

OPERATION The operation of the present swim fin may best be understoodwith reference to FIG. 1, which shows the fin mounted on the foot l2ofawearer who is swimming in a facedown position. FIG. 1 illustrates thecondition which occurs when the wearer is moving forwardly through thewater and is simultaneously kicking downwardly the foot and leg portionillustrated in the drawing, the direction of kicking being indicated bythe arrow C. ,y j

The illustrated downstroke creates thrust, and also generates relativelyhigh pressure regions H.P.l and H.P.2

along the downwardly facing surface of the blade 10, namely along andadjacent the top wall 22. The downstroke also causes a certain amount ofupward flexing of the blade, espedaily at portions thereof relativelyadjacent the tip (namely, portions remote from wall means vl3). h

At the same time that downward kicking is occurring, as indicated by thearrow C, the swimmer is moving forwardly through the water, withconsequent flow of water rearwardly along the blade walls 22 and and asindicated, respectively, by arrows 31 and 32. Such forward movement ofthe swimmer is the result of the indicated kicking action which kickinggenerates two important effects as described in the followingparagraphs. 7 v I The first effect is direct thrust of the blade wall 22against the water. Such thrust, when the fin is in the position shown inFIG. 1, has vertical and horizontal components, and only the latter isoperative to produce forward propulsion of the swimmer through thewater. It is emphasized that the horizontal component of direct thrustis greatest adjacent the highpressure region H.P.l, since the portion ofwall 22 adjacent such region is inclined sharply upwardly. Conversely,there is very little horizontal component of direct thrust adjacenthighpressure region H.P.2, since the fin is, when in the FIG. 1position, only very slightly inclined adjacent such region.

After the fin has moved downwardly (from the FIG. 1 position) until allportions thereof are generally horizontal, there is very little or nohorizontal component of direct thrust.

The second effect is different from the direct-thrust effect describedabove, and instead is jet thrust. The jet thrust effect results fromconverting the relatively no-work" region adjacent area H.P.2 into auseful jet pump. Such pumpf' causes flow of water through passages24-26, as shown by arrows 33, with consequent jet thrust action at theblade tip. In addition, such pump" augments the flow along the bladesurfaces and as indicated by arrows 31 and 32.

The water scoop (mouth or intake) openings 28 at the forward ends ofnozzle passages 24-26 face in the general direction of blade movement inresponse to the downward blade-kicking indicated by arrow C. This isbecause the waterscoop openings 28 are directed transversely to theplane of blade 10 (FIG. 3). Therefore, the high pressure at region H.P.2is very effective in causing flow (arrows 33) into and through nozzlepassages 24-26. The water entering such passages passes around a gentlecorner (surfaces 29 and 30) and then accelerates efficiently (alongpaths generally in the plane of blade 10) until it discharges at highspeed through jet-exhaust openings 27. Such acceleration results fromthe progressively decreasing cross-sectional areas of the passages 24-26as the exhaust openings or orifices 27 are approached. The direction ofjet exhaust is away from the foot and ankle of the wearer, namely, awayfrom mounting means 1 1.

The water jetting through exhaust openings 27 creates substantial thrusthaving a major horizontal component, with consequent increasedpropulsion of the swimmer in a forward direction. It is emphasized thatsuch jet thrust is still present when the swim fin is generallyhorizontal, at which time there is, as stated above, little or no directthrust.

Because the jet-exhaust openings are at the tip of blade 10, anentrainment or drag effect is generated whereby blade surface flow(shown by arrows 31 and 32) is augmented. The water jetting fromorifices 27 (upper arrow 33, FIG. 1) entrains or drags the water passingrearwardly off blade walls 22 and 20 and as shown by upper arrows31 and32. Such entrainment or dragging generates a relatively low-pressureregion v adjacent the blade tip, and such low-pressure region makes iteasier for water to flow rearwardly off the blade walls. It follows thatthere are three layers of jets off the blade tip, as shown by the upperarrows 31-33, and these three jet layers augment the propulsive action:which moves the swimmer.

In addition to the above, the tip-located jets from passages 24-26 serveto'minimize the turbulence and vortexing which is inherently present atthe blade tip due to the kicking action. The result is greaterefficiency of propulsion.

Because the jets are through the tip-located orifices 27, instead ofthrough the bottom wall 20, there is a relatively greater thrust in thehorizontal (useful) direction. For example, and referring to FIG. 1, theuppermost arrow 33 is much closer to the horizontal than would be anycorresponding arrow representing flow through bottom wall 20. On theother hand, the jet exhaust representedby the uppermost arrow 33 in FIG.1 is not to a high pressure region, as would be the case if dischargewere through top wall 22 adjacent region H.Pl. However, this does notimply that the tip-located orifices 27 may not be inclined away from theplane of the tip region of blade 10. They may, for example, be inclinedin a direction somewhat counterclockwise from that shown in FIG. 1, withconsequent reduction of the angle between uppermost arrow 33 and thehorizontal.

It is emphasizedthat the jets from orifices 27 are directed into themain body of water and not against or adjacent any portion of the finitself. In the prior art, on the other hand, any jets were substantiallyforward of the tip region of the fin, which diminished the propulsiveaction created by the jets.

During the upstroke --(not shown) of the foot of the swimmer, relativelylittle propulsive force is created, and relatively little effective workis done. It is to be noted, however, that the entire upper surface ofthe blade (as shown in FIG. 1

namely the bottom wall 20, is smooth and is not provided with orificesor ports which tend to create drag.

The foregoing detailed description is to be clearly understood as givenby way of illustration and example only, the spirit and scope of thisinvention being limited solely by the appended claims.

I claim:

1. A swim fin, which comprises:

wall means to define a foot pocket,

first and second side ribs extending forwardly from said foot pocketwall means,

at least portions of said side ribs diverging relative to each other ina direction away from said foot pocket wall means, and

wall means extending between said side ribs and forming the blade of theswim fin, at least part of said blade wall means being a top wall,

said top wall terminating, at the inner end portion thereof relativelyadjacent said foot pocket wall means, at an inner edge which is spacedfrom said foot pocket wall means, said top wall terminating, at theouter end portion thereof remote from said foot pocket wall means, in aregion which is adjacent the tip of said blade, at least part of saidblade wall means being a bottom wall which is spaced from said top wall,said bottom wall terminating, at the outer end portion thereof remotefrom said foot pocket wall means, in a region which is adjacent the tipof said blade, said top and bottom walls cooperating with each other indefining at least one water passage, said water passage terminating atits inner end in a water-scoop opening which is defined in part by saidinner edge of said top wall, said water passage terminating at its outerend in a jetexhaust orifice which is defined between said outer endportions of said top and bottom walls, said orifice being directed awayfrom said foot pocket walls means.

2. A swim fin, which comprises:

a blade adapted to be employed in propelling a swimmer through thewater,

means provided at one end of said blade to mount the same to the footofa swimmer,

water-scoop means provided on the top of said blade and directed toreceive water in response to downward movement of the foot of saidswimmer when said swimmer is in a face-down position,

said water-scoop means being disposed relatively adjacent said mountingmeans,

jet-exhaust means provided at the other end of said blade remote fromsaid mounting means, said jet-exhaust means being directed to dischargewater in a direction away from said mounting means, said jet-exhaustmeans comprising orifice means disposed at the extreme tip of said otherend of said blade, said tip being the portion of said blade most remotefrom said mounting means, and passage means to conduct water from saidwater-scoop means to said jet-exhaust means for discharge through thelatter, said passage means comprising at least one nozzle passagethrough said blade, the walls of said nozzle passage being shaped toeffect acceleration of water passing from said water-scoop means to saidjet-exhaust means, said shaping being such that said nozzle passage hasa cross-sectional area which decreases progressively in a directiontoward said jet-exhaust means, and throughout substantially the entiredistance from said water-scoop means to said jet-exhaust means.

3. A swim fin, which comprises:

a blade adapted to be employed in propelling a swimmer through thewater,

means provided at one end of said blade to mount the same to the foot ofa swimmer,

water-scoop means provided on the top of said blade and directed toreceive water in response to downward movement of the foot of saidswimmer when said swimmer is in a face-down position,

said water-scoop means being disposed relatively adjacent said mountingmeans,

jet-exhaust means provided at the other end of said blade remote fromsaid mounting means,

said jet-exhaust means being directed to discharge water in a directionaway from said mounting means, and

passage means to conduct water from said water-scoop means to saidjet-exhaust means for discharge through the latter,

said passage means being defined in part by upper and lower walls whichextend from said water-scoop means to said other end of said blade andsubstantially separate the water flowing through said passage means fromthe water passing along the exterior of said blade.

4. The invention as claimed in claim 1, in which said jet-exhaust meanscomprises orifice means disposed at the extreme tip of said other end ofsaid blade, said tip being the portion of said blade most remote fromsaid mounting means.

5. The invention as claimed in claim 1, in which said passage meanscomprises at least one nozzle passage through said blade, the walls ofsaid nozzle passage being shaped to effect acceleration of water passingfrom said water-scoop means to said jet-exhaust means.

6. The invention as claimed in claim 5, in which said nozzle passage hasa cross-sectional area which decreases progressively in a directiontoward said jet-exhaust means, and throughout substantially the entiredistance from said waterscoop means to said jet-exhaust means.

7. The invention as claimed in claim 1, in which the mouth of saidwater-scoop means is directed transversely to the plane of said blade.

8. The invention as claimed in claim 7, in which the walls of saidpassage means include smoothly-curving portions adapted to change thedirection of flow of water from said direction transverse to the planeof said blade to a direction in the plane of said blade.

9. A swim fin, which comprises:

wall means to define a foot pocket,

first and second side ribs extending forwardly from said foot pocketwall means,

at least portions of said side ribs diverging relative to each other ina direction away from said foot pocket wall means,

intermediate rib means located between said first and second side ribsand extending forwardly from said foot pocket wall means,

a top wall connected to said side ribs and to said intermediate ribmeans,

said top wall extending to the tip of said blade,

said top wall forming the top surface of the blade of said fin,

said top wall terminating, at the inner portion thereof relativelyadjacent said foot pocket wall means, in inner edges which are spacedforwardly from said foot pocket wall means, and

a bottom wall connected to said side ribs and to said intermediate ribmeans, said bottom wall extending to the tip of said blade, said bottomwall forming the bottom surface of the blade of said fin, said bottomwall being spaced from said top wall, at least portions of said bottomwall extending to said foot pocket wall means, said top and bottom wallscooperating with said side ribs and with said intermediate rib means indefining a plurality of water passages, each of said water passagesterminating at its inner end in a water-scoop opening which is definedin part by one of said inner edges of said top wall,

each of said water passages terminating at its outer end in ajet-exhaust orifice which is defined at the tip of said blade betweenthe extreme outer edges of said top and bottom walls, said orifice beingdirected away from said foot pocket wall means.

10. The invention as claimed in claim 9, in which said top and bottomwalls converge toward each other in a direction away from said footpocket wall means, whereby to effect progressive acceleration of waterpassed therethrough from said water-scoop opening to said jet-exhaustorifice.

11. The invention as claimed in claim 10, in which said first and secondside ribs, and said intermediate rib means, taper convergently andprogressively in a direction away from said foot pocket wall means.

12. The invention as claimed in claim 10, in which the portion of saidbottom wall which is closer to said foot pocket wall means than are saidinner edges of said top wall is curved in a concave manner to deflectwater around a corner from said water-scoop openings to said jet-exhaustorifices.

13. The invention as claimed in claim 9, in which foot pocket wallmeans, said side ribs, said rib means, and said top and bottom walls areformed integrally of a single mass of elastomeric material.

14. The invention as claimed in claim 9, in which said first and secondribs and said intermediate rib means include portions which extend,respectively, above and below said top and bottom walls, such extensionportions serving to direct water along the exterior surfaces of said topand bottom walls.

15. The invention as claimed in claim 9, in which said intermediate ribmeans comprises two parallel ribs spaced from each other.

16. The invention as claimed in claim 9, in which the crosssectionalshape of each of said water passages is rectangular.

17. The invention as claimed in claim 16, in which said cross-sectionalshape, at blade regions remote from said foot pocket wall means, is widein the dimension between said ribs and thin in the dimension betweensaid top and bottom walls.

Disclaimer 3,649,979.D0uglas K. MapNeil, Costa Mesa, Calif. SWIM FIN.Patent dated Mar. 21, 1972. Dlsclaimer filed Oct. 11, 1974, by theassignee, US.

Divers 0o. Hereby enters this disclaimer to claims 1, 3, 4, 7 8, 9, 13,16 and 17 of said patent.

[Ojfioz'al Gazette November 26, 1974.]

1. A swim fin, which comprises: wall means to define a foot pocket,first and second side ribs extending forwardly from said foot pocketwall means, at least portions of said side ribs diverging relative toeach other in a direction away from said foot pocket wall means, andwall means extending between said side ribs and forming the blade of theswim fin, at least part of said blade wall means being a top wall, saidtop wall terminating, at the inner end portion thereof relativelyadjacent said foot pocket wall means, at an inner edge which is spacedfrom said foot pocket wall means, said top wall terminating, at theouter end portion thereof remote from said foot pocket wall means, in aregion which is adjacent the tip of said blade, at least part of saidblade wall means being a bottom wall which is spaced from said top wall,said bottom wall terminating, at the outer end portion thereof remotefrom said foot pocket wall means, in a region which is adjacent the tipof said blade, said top and bottom walls cooperating with each other indefining at least one water passage, said water passage terminating atits inner end in a waterscoop opening which is defined in part by saidinner edge of said top wall, said water passage terminating at its outerend in a jetexhaust orifice which is defined between said outer endportions of said top and bottom walls, said orifice being directed awayfrom said foot pocket walls means.
 2. A swim fin, which comprises: ablade adapted to be employed in propelling a swimmer through the water,means provided at one end of said blade to mount the same to the foot ofa swimmer, water-scoop means provided on the top of said blade anddirected to receive water in response to downward movement of the footof said swimmer when said swimmer is in a face-down position, saidwater-scoop means being disposed relatively adjacent said mountingmeans, jet-exhaust means provided at the other end of said blade remotefrom said mounting means, said jet-exhaust means being directed todischarge wateR in a direction away from said mounting means, saidjet-exhaust means comprising orifice means disposed at the extreme tipof said other end of said blade, said tip being the portion of saidblade most remote from said mounting means, and passage means to conductwater from said water-scoop means to said jet-exhaust means fordischarge through the latter, said passage means comprising at least onenozzle passage through said blade, the walls of said nozzle passagebeing shaped to effect acceleration of water passing from saidwater-scoop means to said jet-exhaust means, said shaping being suchthat said nozzle passage has a cross-sectional area which decreasesprogressively in a direction toward said jet-exhaust means, andthroughout substantially the entire distance from said water-scoop meansto said jet-exhaust means.
 3. A swim fin, which comprises: a bladeadapted to be employed in propelling a swimmer through the water, meansprovided at one end of said blade to mount the same to the foot of aswimmer, water-scoop means provided on the top of said blade anddirected to receive water in response to downward movement of the footof said swimmer when said swimmer is in a face-down position, saidwater-scoop means being disposed relatively adjacent said mountingmeans, jet-exhaust means provided at the other end of said blade remotefrom said mounting means, said jet-exhaust means being directed todischarge water in a direction away from said mounting means, andpassage means to conduct water from said water-scoop means to saidjet-exhaust means for discharge through the latter, said passage meansbeing defined in part by upper and lower walls which extend from saidwater-scoop means to said other end of said blade and substantiallyseparate the water flowing through said passage means from the waterpassing along the exterior of said blade.
 4. The invention as claimed inclaim 1, in which said jet-exhaust means comprises orifice meansdisposed at the extreme tip of said other end of said blade, said tipbeing the portion of said blade most remote from said mounting means. 5.The invention as claimed in claim 1, in which said passage meanscomprises at least one nozzle passage through said blade, the walls ofsaid nozzle passage being shaped to effect acceleration of water passingfrom said water-scoop means to said jet-exhaust means.
 6. The inventionas claimed in claim 5, in which said nozzle passage has across-sectional area which decreases progressively in a direction towardsaid jet-exhaust means, and throughout substantially the entire distancefrom said water-scoop means to said jet-exhaust means.
 7. The inventionas claimed in claim 1, in which the mouth of said water-scoop means isdirected transversely to the plane of said blade.
 8. The invention asclaimed in claim 7, in which the walls of said passage means includesmoothly-curving portions adapted to change the direction of flow ofwater from said direction transverse to the plane of said blade to adirection in the plane of said blade.
 9. A swim fin, which comprises:wall means to define a foot pocket, first and second side ribs extendingforwardly from said foot pocket wall means, at least portions of saidside ribs diverging relative to each other in a direction away from saidfoot pocket wall means, intermediate rib means located between saidfirst and second side ribs and extending forwardly from said foot pocketwall means, a top wall connected to said side ribs and to saidintermediate rib means, said top wall extending to the tip of saidblade, said top wall forming the top surface of the blade of said fin,said top wall terminating, at the inner portion thereof relativelyadjacent said foot pocket wall means, in inner edges which are spacedforwardly from said foot pocket wall means, and a bottom wall connectedto said side ribs and to said intermedIate rib means, said bottom wallextending to the tip of said blade, said bottom wall forming the bottomsurface of the blade of said fin, said bottom wall being spaced fromsaid top wall, at least portions of said bottom wall extending to saidfoot pocket wall means, said top and bottom walls cooperating with saidside ribs and with said intermediate rib means in defining a pluralityof water passages, each of said water passages terminating at its innerend in a water-scoop opening which is defined in part by one of saidinner edges of said top wall, each of said water passages terminating atits outer end in a jet-exhaust orifice which is defined at the tip ofsaid blade between the extreme outer edges of said top and bottom walls,said orifice being directed away from said foot pocket wall means. 10.The invention as claimed in claim 9, in which said top and bottom wallsconverge toward each other in a direction away from said foot pocketwall means, whereby to effect progressive acceleration of water passedtherethrough from said water-scoop opening to said jet-exhaust orifice.11. The invention as claimed in claim 10, in which said first and secondside ribs, and said intermediate rib means, taper convergently andprogressively in a direction away from said foot pocket wall means. 12.The invention as claimed in claim 10, in which the portion of saidbottom wall which is closer to said foot pocket wall means than are saidinner edges of said top wall is curved in a concave manner to deflectwater around a corner from said water-scoop openings to said jet-exhaustorifices.
 13. The invention as claimed in claim 9, in which foot pocketwall means, said side ribs, said rib means, and said top and bottomwalls are formed integrally of a single mass of elastomeric material.14. The invention as claimed in claim 9, in which said first and secondribs and said intermediate rib means include portions which extend,respectively, above and below said top and bottom walls, such extensionportions serving to direct water along the exterior surfaces of said topand bottom walls.
 15. The invention as claimed in claim 9, in which saidintermediate rib means comprises two parallel ribs spaced from eachother.
 16. The invention as claimed in claim 9, in which thecross-sectional shape of each of said water passages is rectangular. 17.The invention as claimed in claim 16, in which said cross-sectionalshape, at blade regions remote from said foot pocket wall means, is widein the dimension between said ribs and thin in the dimension betweensaid top and bottom walls.